1. FIELD OF THE INVENTION
This invention relates to improvements in or relating to a combustion type heater for an automotive room heating system.
2. DESCRIPTION OF THE PRIOR ART
In an automotive passenger compartment heating system, waste heat of engine cooling water or the like is utilized as a heat source. In the case of a bus or the like which is intended to be used in a cold district, however, since the heated load is relatively great as compared with the amount of heat emanating from the engine, a special heat source which results from combustion of petroleum fuel such as kerosene, light oil or the like is utilized for heating the passenger compartment. Alternatively, a combustion type heater is installed which is independently operable whether the engine is running or stopped.
An example of a combustion type heater is shown in FIGS. 1 through 3 of the accompanying drawings, wherein air introduced into a box-like casing 1 through an air inlet portion 3 formed by a wire gauze or the like mounted on the top wall of the casing 15 is admitted through an admission port 4 into and pressurized in an air blower 2 which is centrally disposed in the casing 1 and driven by means of an electric motor or the like (not shown); and the air thus pressurized is fed from the air blower 2 into a combustor 6 through an air hose 5. The admission port 4 is disposed inside the casing 1 to prevent it from being clogged with snow and/or ice. Meanwhile, fuel from an external fuel tank (not shown), while being passed through fuel pipes 7 and 8, is pressurized by an electromagnetic fuel pump 9 and then fed to the combustor 6. The fuel thus fed to the combustor 6 is ignited by an ignition plug 10. A heat exchanger 11 integral with the combustor 6 is provided in which engine cooling water, for example, is heated by combustion gas which results from the combustion of the fuel.
Engine cooling water is introduced, through a cooling water inlet port 12, into the heat exchanger 11 by means of a water pump 13, sufficiently heated in the heat exchanger, and then passed, via a cooling water output port 14, to a heater core (not shown) provided for the room heating purposes in the passenger compartment, so that warm air is fed from the heater core to warm up the passenger compartment of the motor vehicle. In this way, an enhanced heating performance can be achieved when the motor vehicle is used in a cold district where heat from the engine alone is not sufficient to satisfactorily warm up the passenger compartment of the motor vehicle. The water pump 13 is driven, like the air blower 2, by means of an electric motor energized by a battery.
However, the aforementioned conventional combustion type heater is disadvantageous in that since air for combustion is introduced only through the air inlet port 3 provided at the top of the casing 1, the air thus introduced tends to stagnate in a lower portion of the casing 1 and to be heated by heat irradiated from the combustor 6 and so forth so that the temperature of the surrounding components tends to be gradually elevated. If the combustion type heater continues to be operated for a long time when the open air temperature is not so low, then the temperature of the fuel pump 9 and so forth will considerably be elevated, as a result of which fuel will be evaporated in the fuel pump 9 and in the neighborhood of the outlet of the pump so that there will occur a so-called vapor lock condition which will in turn cause intermittent fuel supply, thus resulting in the heating power of the heater being weakened and the combustion becoming unstable. Furthermore, if the air inlet port 3 is covered with snow or is frozen, then air introduction effected therethrough will become difficult so that the air blower and so forth will be overloaded and thus subjected to failure such as by seizure, short or the like.